Ceramic ware support for use in kilns



Feb. 3, 1959 G. J. EASTER 2,871,543

CERAMIC WARE SUPPORT FbR USE IN KILNS Filed May 20. 1955 2,871,543 CERAMIC WARE SUPPORT FOR USE IN KILNS George J. Easter, Buffalo, N. Y., assignor to Electro Refractories & Abrasives Corporation, Buffalo, N. Y.

Application May 20, 1955, Serial No. 509,747

8 Claims. (Cl. 25-153) This invention relates to an improvement in kiln furniture used to support ceramic ware in kilns while the ware is being fired.

One object of the invention is to reduce the cost of the kiln furniture; another is to eliminate the difficulties arising from the oxidation and growth of silicon carbide United States Patent refractories used for similar purposes; another is to provide maximum useful space between supports for setting ware to be fired. Other objects will be obvious from the following description.

In placing ceramic ware to be fired in a kiln, and particularly a tunnel kiln, it is commonly supported on slabs or batts which constitute shelves. The shelves in turn are supported at three or more points on posts which rest on the shelf beneath or on the upper refractory member of the kiln car or base. The shelves are made of silicon carbide, or in the case of lower temperature kilns, of fireclay, mullite and the like. Two or more shelf slabs frequently share a common support at a corner.

The posts also have been made of silicon carbide or of the less refractory materials. In order to assure stability to the structure, the posts have been made with relatively large bases and tops. The intervening portion of the post has either been of the same cross section as the bottom and top, or, in the case of silicon carbide posts, has been cut away to give the post an I-shaped vertical section. I

Such silicon carbide posts have been the best available but have had a potential fault in that over a long period of service they oxidize slowly and as a result grow. This growth weakens the post somewhat, and what is more serious, changes the length of the post so that if a car structure is disassembled, the posts have to be carefully matched .for length before the car superstructure can be re-assembled. There have even been instances reported where the growth has been so great that the upper deck has had to be permanently removed for the car to be able to pass through the kiln. This, of course, results in an uneconomic loss of kiln capacity.

Any unevenness of growth between posts supporting a single slab is very serious in that it causes uneven support to be exerted which may result in tipping or slipping or even breakage of the slab. Where more than three points of support per batt are used, the effect of uneven lengths of supporting posts is to make the fourth support completely ineffective and thus incur serious danger of the loaded shelf tipping in service and damaging the ware set on it.

As a result of these objections to silicon carbide posts, repeated efforts have been made to use oxidic refractory posts composed of alumina or more often of mullite or super-refractory fireclay at temperatures higher than those at which these materials are satisfactory. This has resulted in very poor service particularly where the end of the post is shared by two or more batts resting thereon. In the case of such shared posts, the end of the post is found to be simply pulled apart by the tensile forces we ice 2 set up by thermal expansion and the irregular weaving motion characteristic of kiln car superstructures during passage through the kiln. Somewhat similar failure occurs even when only one batt rests on such a post dueto collapse of the post which tends to split or shear, starting at the end.

The peculiar splitting apart of the ends of shared posts led me to attempt to cure the trouble by simply placing a thin flat block of silicon carbide refractory (which has very high tensile strength) between the end of the post proper and the batts resting thereon. This proved an inadequate solution, however, as the'posts continued to collapse by failure at their ends underneath the silicon carbide block. 1

I found, howevetg that when the ends of the post were encased in a collar of high tensile strength material which also extended across the end of the post in a sort of balland-socket structure, the collapse of the post under shared post loading did not occur until substantially higher temperatures or heavier loads were applied. When used in this way, the cross section of the post proper can at times be made in tubular form rather than solid, with a saving in material and heat capacity of up to one-third. Solid post portions can, of course, obviously be used when desired.

In the accompanying drawings:

Fig. l is an elevation, partly in section, of a post assembly embodying, my invention with portions of warecarrying slabs above and below the post.

Fig. 2 is a sectional elevation of the upper portion of a post assembly of modified construction. 7

In the construction illustrated in Fig. l, 1 represents a deck composed of Ware-carrying slabs of silicon carbide or other suitable refractory material supporting a hollow post 3 on an end cap 4. A similar end cap 4a in turn supports the next deck of slabs 2 similar'to' deck 1. Post 3- is made of alumina or of an aluminum silicate refractory, such as mullite or high grade fireclay, and caps 4 and 4a of silicon carbide refractory. In the caps are recesses S entering from the small end of the caps. The diameter of recess 5 is slightly larger than the diameter of post 3 so that the two form a slip fit. Before assembly, the ends of post 3 can be dipped into a suspension of kaolin or other fine refractory material in water, so as to form a tight seal 6 between post and cap. presence of this seal is not always essential, 'but is preferable as a safety measure if the fit between post and caps is not snug. Note, however, that it should be omitted in the structure shown in Fig. 2 in order to enable the interfit between post and socket to be adjusted properly.

In Fig. 2 a special design is shown in cap 41), in which a spherical surface 8 is provided at the bottom of recess 5 against which another spherical surface 9 composing the end of a columnar post 7 rests. The radii of surfaces 8 and 9 should be the same, the surface of the recess be ing originally pressed to shape and that of column 7 being formed on the post before firing. With posts of this sort some angular adjustment between the parts of the post is possible, giving more flexibility to a setting which might include a batt which is warped and hence does not rest in the ideal flat position.

After assembly in the manner shown, the car is simply loaded with ware and put into use. Refractory cement may be used between slabs 1 and 2 and caps 4, if desired, but is not normally necessary, particularly on cars built with so-called three-point support.

With posts of my improved design, the thickness of the SiC web portion resting on the end of the post is so small that even in cases of severe oxidation, the overall height of the post is changed so little that it can be neglected in reassembling posts which have been disassembled for any reason.

My invention is not concerned with the specific compositions of the various refractory parts used, since I find that ordinary commercial refractory compositions of the various types are adequate. The alumina, mulite or fireclay portions may be either extruded or individually molded from compositions well known in their respective arts. The silicon carbide may be of the types disclosed in United States Patents No. 1,204,211 or 1,873,071, or other well known compositions consisting of 80 percent plus of silicon carbide bonded with refractory clay or with silica from oxidation of fine SiC, etc.

I find that these various silicon carbide compositions have tensile strengths of 1,000 to 1500 p. s. i. temperatures up to at least 2450 degrees F. I believe that it is this high tensile strength which enables them to resist the splitting tendencies which disrupt the less refractory portions of any posts unless their ends are encased in the stronger material.

To secure the advantages of my improved construction, I- find it desirable that the vertical depth of recess 5 should be from one-half to one inch in the case of posts two inches or less in diameter and proportionately more with posts of greater diameter, the desirable ratio of diameter to depth of the recess being from 2:1 to 4:1. The outer diameter of the cap should be from approximately one and one-half times to double the diameter of the recess.

While I have disclosed and prefer to use silicon carbide refractories as the material for my caps, it is within the broad scope of my invention to use other high tensile strength refractories such as those made from fine aluminum oxide fired to Cone 23 or higher to vitrify it, imparting tensile strength of 1000 p. s. i. or better at 2450 degrees F.

Having thus disclosed my invention with sufiicient detail to permit its practice by those skilled in the refractories art,

I claim:

1. A ceramic ware support for use in kilns including a column of oxidic refractory material selected from the group consisting of alumina, aluminum silicate and fireclay, and supporting caps having portions which telescope about the ends of said column and confining said ends against splitting lengthwise thereof, said caps being made of refractory material having a tensile strength of at least 1000 p. s. i. at temperatures up to 2450 degrees F., said caps surrounding the said end laterally.

2. A ceramic ware support according to claim 1, in which the caps are composed of at least 80 percent SiC.

-3. A column of aluminum silicate refractory and supporting caps contacting and completely surrounding the ends thereof, said caps being. made of refractory material having a tensile strength of at least 1000 p. s. i. at temperatures up to 2450 degrees F. 1

4. A ceramic ware support including a hollow tubular column of aluminum silicate refractory and silicon carbide caps recessed to receive and support the ends of said column, said caps telescoping about said ends of said column and confining said ends against splitting lengthwise thereof.

5. A Ware supporting structure for ceramic kilns, in-

cluding ware supporting batts and supports therefor, said supports comprising aluminum silicate columns and recessed silicon carbide caps therefor, said caps extending along the outside of said columns and completely around the ends thereof.

6. In a ceramic ware support, a column of aluminum silicate refractory and a silicon carbide cap therefor which completely surrounds the end of said column, said cap having a recess for receiving and supporting said column and being in diameter from one and one-half to two times the diameter of the recess, the diameter of said recess being from two to four times its depth.

7. In a ceramic ware support, a column of aluminum silicate refractory having a spherical surface at an end thereof and a recessed silicon carbide cap therefor which completely surrounds the end of said column, the inner surface of the recess in said cap having a partly spherical surface of the same curvature as that of the end of the column, whereby the column and the cap may be placed in firm contact at a variable angle to one another with relation to the horizontal.

8. A column for supporting a plurality of batts in the firing of ceramic ware consisting of a cylinder of aluminum silicate refractory completely surrounded at each end by a cap of silicon carbide refractory. recessed to receive and closely support said .cylinder, said cap extending laterally from 1 /2 to 2 times the diameter of the recess therein, thereby forming a seat for contact with said batts.

References Cited in the file of this patent UNITED STATES PATENTS 1,466,213 Teetor Aug. 28, 1923 1,665,631 Laschenski Apr. 10, 1928 1,969,126 Forse Aug. 7, 1934 2,629,917 Lovatt Mar. 3, 1953 FOREIGN PATENTS 340,376 Great Britain Jan. 1, 1931 534,546 Great Britain Mar. 10, 1941 

1. A CERAMIC WARE SUPPORT FOR USE IN KILNS INCLUDING A COLUMN OF OXIDIC REFRACTORY MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALUMINA, ALUMINUM SILICATE AND FIRECLAY, AND SUPPORTING CAPS HAVING PORTIONS WHICH TELESCOPE ABOUT THE ENDS OF SAID COLUMN AND CONFINING SAID ENDS AGAINST SPLITTING LENGHTWISE THEREOF, SAID CAPS BEING MADE OF REFRACTORY MATERIAL HAVING A TENSILE STRENGTH OF AT LEAST 1000 P. S. I. AT TEMPERATURE UP TO 2450 DEGREES F., SAID CAPS SURROUNDING THE SAID END LATERALLY. 